Recently, a wireless door locking/unlocking mode where a door of a vehicle is locked or unlocked by remote control becomes widespread, and hence an antenna device for the vehicle and a communication system using the antenna device are used. Such wireless mode requires an antenna device that allows a driver to certainly remotely control the door within a predetermined distance range from the vehicle and a communication system using the antenna device.
A conventional antenna device for a vehicle employed for the wireless mode and a communication system using the antenna device are described hereinafter with reference to FIG. 11 and FIG. 12.
FIG. 11 is a schematic diagram of a conventional general communication system for locking or unlocking door 51 of vehicle 50 in wireless mode. Antenna device 52 for transmitting or receiving radio waves to communicate with the outside is built in mirror movable unit 54. Mirror movable unit 54 is mounted to mirror fixing unit 53 disposed in door 51 of vehicle 50. Mirror movable unit 54 is opened or closed automatically or manually. In other words, the driver operates a switch in the vehicle to automatically open or close mirror movable unit 54, or the driver manually and directly operates mirror movable unit 54 to open or close it.
External communication device 56 communicates with antenna device 52 interactively. External communication device 56 is specific to vehicle 50 and transmits a code or the like specific to vehicle 50. The shape of external communication device 56 is a card shape for example, and is selected to allow the driver to carry the device even when the driver goes away from vehicle 50.
Antenna device 52 is connected to an electronic circuit (not shown) of an internal communication device installed in vehicle 50. The electronic circuit processes information transmitted from external communication device 56, determines whether or not the information is a code specific to vehicle 50, and locks or unlocks the door. The communication system is a combination of external communication device 56, antenna device 52, and the electronic circuit.
Antenna device 52 is formed of a ferrite core, a hollow bobbin into which the core is inserted, a coil wound on the outer periphery of the bobbin, a capacitor, and a resistor. The coil, the capacitor, and the resistor are interconnected in series, and both ends of the connection are electrically connected to the electronic circuit, thereby forming a series resonant circuit. These are not shown.
When all doors 51 of vehicle 50 are closed, and a radio wave is transmitted from external communication device 56 in a state where the driver separates from vehicle 50, antenna device 52 receives the radio wave, the electronic circuit verifies the radio wave against the specific certified code, and locks or unlocks doors 51.
In conventional antenna device 52 and the communication system using the antenna device, however, when the driver of vehicle 50 folds mirror movable unit 54, the direction of antenna device 52 built in mirror movable unit 54 changes. As a result, the directivity of antenna device 52 changes, and hence the driver cannot always and certainly perform the remote control within a predetermined distance range from vehicle 50.
Therefore, a configuration where an antenna device is mounted to the inside of a mirror fixing unit for fixing a mirror, for example, is disclosed in Japanese Patent Unexamined Publication No. 2004-364231. FIG. 12 shows the configuration of this antenna device. In this antenna device, coil 300 is formed by winding a conducting wire on an outer peripheral region of hollow bobbin 200 made of dielectric resin, and ferrite core 100 is inserted into bobbin 200.
Case 400 stores coil 300, capacitor 900, and resistor 110, and they are interconnected by predetermined wiring. Thin lead terminals 500 and 600 made of conductors are insert-molded in case 400. Part other than coil 300, core 100, bobbin 200, capacitor 900, resistor 110, and lead terminals 500 and 600 in case 400 is filled with resin 220 such as silicone.
This antenna device has circuitry where coil 300, capacitor 900, and resistor 110 are interconnected in series and lead terminals 500 and 600 are disposed at both ends of this connection. Lead terminals 500 and 600 are electrically connected to an electronic circuit as the internal communication device disposed in the vehicle body, thereby forming a series resonant circuit.
The antenna device is mounted to the mirror fixing unit of the vehicle, so that the mirror fixing unit does not move even when the driver folds the movable unit of the door mirror. Therefore, the direction of the antenna device in the mirror fixing unit does not change, and hence the directivity of the antenna device does not change before and after the folding.
However, the directivity of the antenna device has a characteristic where the directivity expands from the mounted position as the origin. The driver, in performing the remote control, is apt to carefully watch the door handle rather than the mirror fixing unit. Therefore, when the antenna device is mounted to the inside of the mirror fixing unit, the behavioral characteristic of the driver makes it difficult to obtain high directivity of the antenna device.
While, in Japanese Patent Unexamined Publication No. H9-125776, a wireless door locking/unlocking device is disclosed that can certainly automatically lock a door even when the driver is near the vehicle in getting out and can sufficiently improve secrecy of an identification code. The locking/unlocking device has an antenna device that transmits a signal for starting the external communication device and receives a signal including the identification code transmitted from the external communication device. The locking/unlocking device further has a door lock controlling means for locking or unlocking the door based on the signal received by the antenna device. A door outer handle made of resin is disposed in the door. The antenna device is disposed near the door outer handle, and the communication distance between the antenna device and the external communication device is set at 50 cm or shorter. In this conventional example, a specific mounted position of the antenna device is inside the door outer handle.
Since the communication distance between the antenna device and the external communication device is set at 50 cm or shorter in the conventional example, for operating the locking/unlocking device, the driver must approach the door until this distance. When the antenna device is disposed near the door outer handle, the locking/unlocking device is apt to suffer impact or vibration that is caused by the motion of the driver in operating the door outer handle, and the operation reliability is low.
When the locking/unlocking device is mounted to the vehicle, the resonance frequency shifts dependently on the mounted position and hence this shift is required to be adjusted. However, in the conventional antenna device, this adjustment cannot be easily and accurately performed.
The present invention addresses the conventional problems. The present invention provides an antenna device where the adjusting range of the resonance frequency is large and certain adjustment can be performed, and a communication system allowing the driver to certainly perform the remote control within a predetermined distance range from the vehicle using the antenna device.